Architecture to support network-wide multiple-in-multiple-out wireless communication over a downlink

ABSTRACT

The present invention provides a method of coordinating the downlink transmissions from a plurality of base stations to at least one mobile unit. The method is implemented in a control plane entity and includes receiving, at the control plane entity and from each of the plurality of base stations, channel state information for a plurality of wireless communication channels between the plurality of base stations and one or more mobile units. The method also includes determining, at the control plane entity and based on the channel state information, transmission formats for downlink transmissions from the plurality of base stations to the mobile unit(s). The method further includes providing the transmission formats to the plurality of base stations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/233,253, filed on Sep. 18, 2008, which is entitled, “ANARCHITECTURE TO SUPPORT NETWORK-WIDE MULTIPLE-IN-MULTIPLE-OUT WIRELESSCOMMUNICATION OVER AN UPLINK” This application is related to U.S. patentapplication Ser. No. 11/778,282, filed on Jul. 16, 2007, entitled “ANARCHITECTURE TO SUPPORT NETWORK-WIDE MULTIPLE-IN MULTIPLE-OUT WIRELESSCOMMUNICATION and U.S. patent application Ser. No. 12/233,253, filed onSep. 18, 2008, entitled “AN ARCHITECTURE TO SUPPORT NETWORK-WIDEMULTIPLE-IN-MULTIPLE-OUT WIRELESS COMMUNICATION OVER AN UPLINK

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to communication systems, and, moreparticularly, to wireless communication systems.

2. Description of the Related Art

Base stations in wireless communication systems provide wirelessconnectivity to users within a geographic area, or cell, associated withthe base station. In some cases, the cell may be divided into sectorsthat subtend a selected opening angle (e.g., three 120° sectors or six60° sectors) and are served by different antennas. The wirelesscommunication links between the base station and each of the userstypically includes one or more downlink (DL) (or forward) channels fortransmitting information from the base station to the mobile unit andone or more uplink (UL) (or reverse) channels for transmittinginformation from the mobile unit to the base station.Multiple-input-multiple-output (MIMO) techniques may be employed whenthe base station and, optionally, the user terminals include multipleantennas. For example, a base station that includes multiple antennascan concurrently transmit multiple independent and distinct signals onthe same frequency band to same user or multiple users in a cell/sector.MIMO techniques are capable of increasing the spectral efficiency of thewireless communication system roughly in proportion to the number ofantennas available at the base station.

Conventional MIMO techniques coordinate operation of multiple antennasthat are co-located with the coordinating base station. For example, themultiple antennas associated with a base station (BS) are typicallyconfigured so that the antennas are less than about 10 m from the basestation. The signals transmitted from the base station to the antennasand then over the air interface to the mobile station (MS) on DL may bephase aligned so that they can be coherently combined at the receiver,e.g., the mobile station. Constructive and/or destructive interferenceof coherent radiation from the multiple antennas can therefore be usedto amplify the signal in selected directions and/or null the signal inother directions. Processing of the coherent signals may also be used tominimize the mutual interference between multiple transmitters.Similarly on UL, signals received from multiple antennas can be combinedto maximize signal strength, maximize SINR, detect multiple signalssimultaneously through well-known algorithms such as MRC (maximum ratiocombining), MMSE (minimum mean squared error), and MLSE (maximumlikelihood sequence estimator). However, conventional MIMO does notaddress the inter-cell interference caused by uplink and/or downlinktransmissions in neighboring cells.

A new class of multi-antenna techniques called Inter-Base Station MIMO(IBS-MIMO) has been proposed to enhance air-interface performance byenabling concurrent transmission of superposed signal waveforms fromantennas at different base stations to one or more mobile terminals insuch a way that the resulting mutual interference is suppressed. On thedownlink, different BSs concurrently transmit (in a coordinated fashion)superposed signal waveforms from their antennas to one or more MSs insuch a way that the resulting mutual interference is suppressed and thesignals from multiple BSs may be coherently combined at each MS. In thisprocess, the signal destined for a specific MS can be transmitted fromdifferent BSs. The radio access network provides control signalingand/or data plane exchanges to coordinate the BSs so that theirtransmissions can be coherently combined.

Coordination can be accomplished in different ways to create a range ofIBS MIMO techniques. For example, coordination with the goal ofachieving coherent reception at the MS for transmissions by a pluralityof base stations while suppressing interference caused by transmissionsto other MSs served by the same or different plurality of base stationsis called “Network MIMO”. Network MIMO requires coordination across BSsat short time scales (e.g. on the order of a few ms to tens of ms). Theactual time scales can be determined based on the maximum mobileterminal velocity expected to be supported. On the other hand,coordination to achieve non-coherent combining at the MS is called“Collaborative MIMO” and can be performed at longer time scales on theorder of 100s of ms. Similar architectures can be used to supportNetwork MIMO and Collaborative MIMO even though the two approachesimpose different delay and bandwidth requirements on the network thatconnects the BSs.

Implementation of IBS-MIMO techniques is strongly constrained byexisting network architectures and expected future developments innetwork architectures. Many network architectures support control planeoperations and bearer plane operations. For example, base stations canbe configured to handle bearer plane operations such as physical layerand medium access control layer operations. In some cases, the bearer(or data) plane can be separated into two levels: an upper levelimplemented in an IP gateway router and a lower level implemented in anIP-capable base station. Control plane operations such as scheduling andresource allocation may also be implemented in the base station.IBS-MIMO techniques should be implemented in a manner that is, to thegreatest degree possible, consistent with these architecturalconstraints to minimize disruptions caused by implementation of thesetechniques.

SUMMARY

The disclosed subject matter is directed to addressing the effects ofone or more of the problems set forth above. The following presents asimplified summary of the disclosed subject matter in order to provide abasic understanding of some aspects of the disclosed subject matter.This summary is not an exhaustive overview of the disclosed subjectmatter. It is not intended to identify key or critical elements of thedisclosed subject matter or to delineate the scope of the disclosedsubject matter. Its sole purpose is to present some concepts in asimplified form as a prelude to the more detailed description that isdiscussed later.

In one embodiment, a method is provided for coordinating the downlinktransmissions from a plurality of base stations to at least one mobileunit. The method is implemented in a control plane entity and includesreceiving, at the control plane entity and from each of the plurality ofbase stations, channel state information for a plurality of wirelesscommunication channels between the plurality of base stations and one ormore mobile units. The method also includes determining, at the controlplane entity and based on the channel state information, transmissionformats for downlink transmissions from the plurality of base stationsto the mobile unit(s). The method further includes providing thetransmission formats to the plurality of base stations.

In other embodiments, a method is provided for coordinated downlinktransmission from a plurality of base stations to at least one mobileunit. The method is implemented in a first base station that is one ofthe plurality of base stations. The method includes providing, to acontrol plane entity and from the first base station, channel stateinformation for wireless communication channels between at least oneantenna associated with the first base station and at least one antennaassociated with the mobile unit(s). The method also includes receiving,from the control plane entity and at the first base station,transmission formats for downlink transmissions from the first basestation to the mobile unit(s). The transmission formats are determinedby the control plane entity for the plurality of base stations based onthe channel state information transmitted to the control plane entityand additional channel state information provided to the control planeentity by at least one second base station from the plurality of basestations. The method further includes transmitting data over thedownlink in coordination with the plurality of base stations using thereceived transmission formats.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed subject matter may be understood by reference to thefollowing description taken in conjunction with the accompanyingdrawings, in which like reference numerals identify like elements, andin which:

FIG. 1 conceptually illustrates one exemplary embodiment of a wirelesscommunication system;

FIG. 2 conceptually illustrates one exemplary embodiment of a method ofoperating a control plane entity in the wireless communication systemshown in FIG. 1; and

FIG. 3 conceptually illustrates one exemplary embodiment of a method ofoperating a bearer plane entity and the wireless communication systemshown in FIG. 1.

While the disclosed subject matter is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the disclosed subjectmatter to the particular forms disclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the scope of the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments are described below. In the interest ofclarity, not all features of an actual implementation are described inthis specification. It will of course be appreciated that in thedevelopment of any such actual embodiment, numerousimplementation-specific decisions should be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The disclosed subject matter will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present invention with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe disclosed subject matter. The words and phrases used herein shouldbe understood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

FIG. 1 conceptually illustrates one exemplary embodiment of a wirelesscommunication system 100. In the illustrated embodiment, the wirelesscommunication system 100 includes a backhaul network 105 that may beused to transmit information among the various elements of the wirelesscommunication system 100. As used herein and in accordance with commonusage in the art, the “backhaul network” refers to the transport networkthat carries wireless network related data and control between basestations and control entities such as radio network controllers. Thebackhaul network 105 may operate according to any combination of wiredand/or wireless communication standards and/or protocols. Exemplarystandards and/or protocols that can be used to implement the backhaulnetwork 105 include Frame Relay, ATM, Ethernet, and the like, as well ashigher layer protocols such as ATM, IP, and the like. Techniques foraccessing the backhaul network 105 and/or communicating informationthrough the network 105 are known in the art and in the interest ofclarity only those aspects of these techniques that are relevant to thepresent techniques will be discussed herein.

The wireless communication system 100 is used to provide wirelessconnectivity to one or more mobile units 110 (only one shown in FIG. 1)so that they may access the network 105. Exemplary mobile units 110 mayinclude cellular telephones, personal data assistants, smart phones,pagers, text messaging devices, Global Positioning System (GPS) devices,network interface cards, notebook computers, desktop computers, and thelike. In various alternative embodiments, the mobile units 110 mayinclude a single antenna or a plurality of antennas for communicatingwith the wireless communication system 100.

In the illustrated embodiment, the wireless communication system 100includes a plurality of base stations (BS) 115 that are used to providewireless connectivity to the mobile units 110. Each base station 115 isconfigured to receive downlink information and convert this informationinto a format that can be transmitted to the mobile unit 110 over airinterfaces 120. The base stations 115 are configured to perform physical(PHY) layer processing and medium access control (MAC) layer functions.Since the physical and/or medium access control layer functionality isused to support radio bearers associated with the air interfaces 120,the functionality implemented in the base stations 115 is typicallyreferred to as “bearer plane” functionality. To implement bearer planefunctions, the base stations 115 use transmission formats, transmissiontimes, and packets provided by control plane entities, as discussedherein. Techniques for implementing bearer plane functionality such asphysical and/or medium access control layer functionality in the basestations 115 are known in the art and in the interest of clarity onlythose techniques that are relevant to the present invention will bediscussed herein. Each the station 115 is communicatively coupled to oneor more antennas 125 that may be used to transmit and receive modulatedradio frequency signals over the air interfaces 120.

The base stations 115 are also capable of gathering state informationassociated with communication between the base stations 115 and themobile unit 110. One type of state information is wireless channel stateinformation that indicates the current state of the wirelesscommunication channel(s) supported by the air interfaces 120. The basestation 115 can determine the wireless channel state information usingknown techniques such as measurements of pilot signal gain and phase,signal-to-interference-plus-noise ratios, C/I ratios, and the like.These types of downlink channel state information may be measured bymobile stations (MSs) from each transmit antenna to each receive antennaand feedback to the BS via uplink, or measured directly at the BS basedon uplink signals and used as is in time division duplex (TDD) ortranslated to down link quantities based on appropriate signalprocessing. Another type of state information is queue state informationthat indicates the current state of queues or buffers maintained by thebase stations 115 for storing data before this data is transmitted overthe downlink to the mobile units 110. For example, queue stateinformation may indicate current buffer occupancy, an overflowcondition, an underflow condition, and the like. The state informationcan be transmitted from the base stations 115 to various control planeentities over a backhaul links 130. The base stations 115 are alsoconfigured to receive control signaling over the backhaul links 130.

The control plane entities in the wireless communication system 100include a mobility management and paging element 133. The mobilitymanagement and paging control element 133 may be logical or physical, asin the following examples. In 1xEV-DO and UMTS-HSPA, a physical networkelement called the Radio Network Controller (RNC) serves the controlfunctions as well as bearer plane functions that span the IP layer andLayer 2. The RNC is located between the IP gateway and the base stations115. In WiMAX Profile C, a physical network element called the AccessService Node Gateway (ASN-GW) co-locates the control functions withbearer plane IP gateway functions. The ASN-GW connects with the basestations 115, which serve all the Layer 1 (physical layer) and mostLayer 2 bearer plane functions. LTE-SAE and UMB are similar to WiMAXProfile C in distributing bearer plane functions at layers 1-3. However,control functions may be located on a separate control element calledthe Signaling RNC or Mobility Management Entity (MME), with specifiedinterfaces to the IP gateway as well as the base stations 115. By virtueof managing key functions such as mobility and paging, the mobilitymanagement and paging element 133 is aware of the location of eachmobile unit 110 in the network as well as the “legs” associated with themobile units 110, i.e. the usable wireless connectivity to differentbase stations 115.

The wireless communication system 100 also includes a control planeentity 135 that is used to support concurrent transmission of superposedsignal waveforms from the antennas 125 so that the superposed signalwaveforms combine coherently at the mobile unit 110. Coordinatingtransmission of the signal waveforms in this manner can reduce orsuppress the mutual interference between the signal waveforms. In theillustrated embodiment, this control plane entity is referred to as adownlink network multiple-input-multiple-output (MIMO) controller(DL-NMC) 135. In one embodiment, the downlink network MIMO controller135 may be co-located with the mobility management and paging element133. In another embodiment, the downlink network MIMO controller 135 maybe co-located with one or more base stations 115. In yet anotherembodiment, the downlink network MIMO controller 135 may be one or moreseparate physical network nodes dedicated to NMC functionality. Thus,the downlink network MIMO controller 135 may be implemented as either acentralized entity or as distributed functionality.

In the illustrated embodiment, the base stations 115 provide thecollected state information to the downlink network MIMO controller 135,which then generates control signaling that is provided to the basestations 115 to coordinate downlink communication with the mobile unit110. For example, the network MIMO controller 135 can use the wirelesschannel state information and/or queue state information to computetransmission formats to be used for transmitting downlink informationfrom each base station 115 to the mobile units 110. The computedtransmission formats can then be communicated to the base stations 115over the backhaul links 130. The transmission format may includeparameters such as information block size, error control codes, coderates, modulation orders, antenna beamforming weights, transmit power,orthogonal frequency division multiplexing (OFDM) tones or tiles, andthe like. In many cases, the control plane operations performed by thedownlink network MIMO controller 135 only use information about thechannel states and (optionally) the states of the mobile-specific queuesmaintained at the base stations 115. Consequently, the downlink networkMIMO controller 135 does not necessarily have to have access to theactual packet contents of the downlink transmission queues.

The downlink network MIMO controller 135 may also participate inselecting the base stations 115 that are part of the downlinkcoordination cluster for each mobile unit 110. In one embodiment, thedownlink network MIMO controller 135 determines membership incoordination clusters for each mobile unit 110 based on informationprovided by the various base stations 115. Membership may bepredetermined and/or dynamically determined by the downlink network MIMOcontroller 135. Alternatively, cluster membership may be determined byother entities in the network 100 such as the base stations 115. Oncemembership in the coordination clusters has been determined,communication channels over the backhaul links 130 may be set up so thatthe state information can be transmitted from the base stations 115 tothe downlink network MIMO controller 135 and control information can betransmitted back to the base stations 115.

In one embodiment, the coordination cluster associated with each mobileunit 110 may be initially determined when the mobile unit 110 firstaccesses the network 100. For example, the downlink network MIMOcontroller 135 (and/or other entities in the network 100) may determinewhether a particular mobile unit 110 can benefit from application ofnetwork MIMO techniques. If the mobile unit 110 is handled using networkMIMO, the downlink network MIMO controller 135 can select thecoordination cluster for the mobile unit 110. In some cases, the mobileunit 110 may be handled by a single base station 115 instead of beingassociated with a coordination cluster. The downlink network MIMOcontroller 135 may also periodically update the status of the mobileunit 110. Updating may include modifying base station membership in thecoordination cluster associated with the mobile unit 110, changing thestatus of the mobile unit 110 to apply network MIMO techniques, changingthe status of the mobile unit 110 to deactivate application of networkMIMO techniques, and the like.

The wireless communication system 100 may include multiple coordinationclusters that are controlled by different downlink network MIMOcontrollers 135. In one embodiment, each cluster consists of one or moredownlink network MIMO controllers 135 and a set of base stations 115that are contiguous in spatial coverage. The geographically neighboringclusters may not overlap unless different sets of frequencies or timeintervals are assigned to different clusters. This separation mayprevent race conditions between downlink network MIMO controllers 135that attempt to control the same base station 115 in the event ofoverlap. If there is separation in terms of frequency sets or timeinterval assignments (even with spatial overlap), such race conditionswould be avoided. In fact, a base station 115 that is capable ofsupporting multiple frequency sets or time interval sets behaves likemultiple base stations 115 and can simultaneously be coordinated bymultiple downlink network MIMO controllers 135, each of which controlsbase stations 115 with a given frequency or time interval. Indeed, withbase stations 115 supporting multiple frequencies or time intervals,spatial overlap may prove to be highly advantageous because a mobileunit 110 within the interior of multiple clusters may get multipleIBS-MIMO benefits, from each of these clusters concurrently.

The wireless communication system 100 also includes an Internet protocolgateway (IP-GW) 140. The IP gateway 140 is predominantly a bearer planedevice that is configured to perform IP layer functions such asproviding downlink packets to the base stations 115 over the backhaullinks 145. However, in some embodiments, the IP gateway 140 may servecontrol plane functions in some deployed standards such as EV-DO andHSPA. The IP gateway 140 and the downlink network MIMO controller 135may communicate over an interface 150. For example, the downlink networkMIMO controller 135 may use the interface 150 to inform the IP gateway140 of the cluster membership for each mobile unit 115. The IP gateway140 may then use this information to ensure that the appropriate basestations 115 are expecting to receive packets destined for the mobileunit 110. Duplicate packet flows may then be transmitted to the basestations 115 that are in the coordination cluster associated with themobile unit 110. The base stations 115 may store the received datapackets in one or more buffers or queues. In one embodiment, themobility management and paging element 133 may be co-located with the IPgateway 140 (as in WiMAX). Alternatively, the mobility management andpaging element 133 may be implemented so that it is physically separatefrom the IP gateway 140 (as in SAE and UMB).

Signals transmitted over the air interfaces 120 should be tightlysynchronized to facilitate the coherent combining of the signals thatare transmitted by the antennas 125. In one embodiment, the downlinknetwork MIMO controller 135 determines timing information for the basestations 115 and the base stations 115 can use this timing informationto coordinate transmission of signals over the air interface 120. Forexample, the timing information may indicate an instant at whichselected information should be transmitted over the air interfaces 120.The base stations 115 may use knowledge of the relative time delaysbetween different branches of the backhaul links from the base stations115 to the antennas 125 to determine when to send signals to theantennas 125. When the base stations 115, the antennas 125, and thebackhaul links are configured so that the relative time delaysassociated with the different backhaul links are known and fixed, thebase stations 115 may determine the relative time delays based on theconfiguration information. However, the stringent timing constraintsimposed by requiring coherency of the signals transmitted and/orreceived by the antennas 125 are likely to require dynamic determinationof the relative time delays. In one embodiment, the base stations 115may dynamically determine the relative time delays between the legs ofthe backhaul links by transmitting a timing signal to the antennas 125,receiving an echo back from the antennas 125, and determining the boththe round-trip delay and one way delays between the base stations 115and antennas 125 based upon a response signal transmitted by theantennas 125 when they receive the timing signal. The timing signals maybe transmitted periodically, in response to initiation of acommunication session with a mobile unit 110, and/or at any other time.

The downlink network MIMO controller 135 may also provide the timinginformation to the IP gateway 140 over the interface 150. In oneembodiment, the IP gateway 140 may use this information to schedulepacket transmissions to the appropriate base stations 115 over thebackhaul links 145. In this way, the IP gateway 140 can ensure thatpackets scheduled for downlink transmission to the mobile units 110 areavailable at the base stations 115 before they are needed for physicallayer processing and eventual transmission over the air interface 120.

The downlink network MIMO controller 135 may be configured to scheduletransmissions over the air interfaces 120. For example, the downlinknetwork MIMO controller 135 may schedule the mobile units 110 thatshould receive data during various downlink transmission time intervals.In one embodiment, the downlink network MIMO controller 135 can jointlyselect the mobile units 110 and compute the transmit formats that areused to transmit information to the selected mobile units 110. However,in alternative embodiments, the scheduling of the mobile units 110 maybe performed by the base stations 115, which then inform the downlinknetwork MIMO controller 135 of the selected mobile units 110. Thedownlink network MIMO controller 135 may then compute transmit formatsand allocates resources for the scheduled downlink transmissions. Thescheduling function could also be distributed between the base stations115 and the downlink network MIMO controller 135 so that some mobileunits 110 may be scheduled by the base stations 115 and the remainingmobile units 110 can be scheduled by the downlink network MIMOcontroller 135.

Although FIG. 1 shows a single downlink network MIMO controller 135,persons of ordinary skill in the art having benefit of the presentdisclosure should appreciate that in practice the wireless communicationsystem 100 may include multiple downlink network MIMO controllers 135,each with its zone of control. The downlink network MIMO controller 135zones may be demarcated spatially to cover a number of base stations 115(such as a city or a suburb) or in other terms such as carrier or tonefrequencies or time intervals used. Depending on preferences indeployment and/or resource management, these zones may overlap asappropriate. Further, as mobile units 110 move through the network, thedownlink network MIMO controllers 135 may have to communicate with eachother to exchange information about these roaming mobile units 110.

FIG. 2 conceptually illustrates one exemplary embodiment of a method 200of operating a control plane entity in the wireless communication systemshown in FIG. 1. One example of a control plane entity includes thedownlink network MIMO controller 135 depicted in FIG. 1. However,persons of ordinary skill in the art having benefit of the presentdisclosure should appreciate that other embodiments of the method 200may be implemented in one or more other control plane entities. In theillustrated embodiment, the control plane entity receives (at 205) stateinformation from bearer plane entities such as base stations. The stateinformation may include wireless communication channel state informationand/or queue state information associated with queues in the basestations.

The control plane entity then determines (at 210) transmission formatsthat can be used by base stations to transmit information over adownlink to one or more mobile units. The transmission formats include,but are not limited to modulation and coding, transmit power, antennaweights, resource blocks (time, frequency, spreading codes and thelike), etc. The transmission formats are determined using the stateinformation provided by the bearer plane entities and are selected (at210) so that base stations can transmit downlink information in acoordinated manner to reduce or suppress mutual interference betweensignals transmitted by the different base stations. In one embodiment,the control plane entity also determines (at 215) individual timinginformation that is used by the base stations and/or their subtendingantennas to coordinate transmissions. The transmission formats and (ifavailable) the timing information are then transmitted (at 220) to thebase stations over one or more backhaul links.

FIG. 3 conceptually illustrates one exemplary embodiment of a method 300of operating a bearer plane entity and the wireless communication systemshown in FIG. 1. In the illustrated embodiment, the bearer plane entityis a base station such as the base stations 115 shown in FIG. 1.However, persons of ordinary skill in the art having benefit of thepresent disclosure should appreciate that other bearer plane entitiesmay be used in other embodiments. The bearer plane entity collects stateinformation, such as channel state information and/or queue stateinformation, and transmits (at 305) the state information to a controlplane entity. The bearer plane entity then receives (at 310)transmission formats for transmitting information to one or more mobileunits. The bearer plane entity may also receive (at 315) timinginformation from the control plane entity. The bearer plane entity thentransmits (at 320) data over the air interface using the transmissionformats and/or timing information provided by the control plane entity.

Referring back to FIG. 1, the downlink network MIMO controller 135 maybe implemented as a centralized entity or as functionality that isdistributed throughout multiple elements (e.g., the base stations 115)within the communication system 100. Embodiments of the communicationsystem 100 that support centralized and distributed embodiments mayutilize different procedures, interfaces, protocols, and/or messages.

A centralized downlink network MIMO controller 135 may use interfacesbetween the base stations 115 and the downlink network MIMO controller135, the base stations 115 and the bearer plane gateway 140, and thedownlink network MIMO controller 135 and the bearer plane gateway 140.Furthermore, protocols can be established for carrying different typesof IBS-MIMO related messages over the interfaces. In some cases, basicinterfaces/messages defined by existing standards can be extended and/ormodified for IBS-MIMO purposes as discussed herein.

For example, the interface between the base stations 115 and the controlplane element is known as S1c in LTE/SAE and U2 in UMB. Since WiMAXProfile C co-locates the control element with the gateway, it does notspecify such a separate interface for the control plane. Persons ofordinary skill in the art should appreciate that known protocols areavailable to form messages to carry information about the locations ofmobile units, active legs, and other information. In one embodiment, theknown protocols could be reused by modifying the known protocols toinclude new IBS-MIMO related messages. For example, the known protocolscould be modified by adding messages that can be used to carry thechannel state information and scheduling parameters from the basestations 115 to the control element 135. The known protocols could alsobe modified to include messages for transmitting schedule grant andtransmission formats information from the control element 135 to thebase stations 115.

Examples of an interface between the base stations 115 and the gateway140 include the S1u in LTE/SAE, U1 in UMB, and R6 in WiMAX. Note that R6also carries control information in WiMAX. In some embodiments, theseknown interfaces and protocols can be modified to include messages tocarry data packets between the base stations 115 and gateway 140. Insome cases, existing messages can be used to carry the new informationso that new messages may not be necessary since no preprocessing of thedata packets is performed at the gateway 140. However, in these cases, anew function may be implemented so that the gateway 140 can distributedata packets destined for the mobile station 110 to each of the basestations 115 that form a leg with the mobile station 110.

Examples of interfaces between the gateway 140 and the control element135 may include the S11 in LTE/SAE and U6 in UMB. Since these areco-located in the ASN-GW in WiMAX Profile C, such an interface isinternal to the ASN-GW. In some embodiments, these known interfaces andprotocols can be modified to include messages to instruct the gateway140 about the legs of each mobile terminal 110, so that the gateway 140can distribute data packets appropriately. New messages may be definedfor this purpose.

In operation, the centralized downlink network MIMO controller 135 mayinitially transmit the locations of various mobile terminals 110 andtheir corresponding legs to the appropriate base stations 115. The corecontrol element 133/135 that manages mobility and paging is aware of thelocation of each mobile terminal 110, as well as all its legs (i.e.,radio links to base stations 115 that satisfy certain pre-determinedcriteria such as link quality over a certain threshold). Thus, the corecontrol element 133/135 can inform each base station 115 of all themobile terminals 110 that have a leg at the base station 115 so that themobile terminal 110 can communicate with the base station 115. Onedistinction between the IBS-MIMO techniques described herein and softhandoff is that it is possible that different measurement thresholds forsoft handoff and IBS-MIMO may result in the number of legs for handoffbeing different than the number of legs that may be used for IBS-MIMO.In this scenario, the mobility manager may be enhanced to maintain aseparate record for IBS-MIMO legs and soft handoff legs and inform thebase stations 115 appropriately.

The centralized downlink network MIMO controller 135 may also controlthe bearer packet distribution within the wireless communication system100. In one embodiment, the control element 135 informs the bearer planegateway 140 (which may be implemented in the RNC in 1xEV-DO and HSPA,IP-GW in LTE/SAE and UMB, and ASN-GW in WiMAX) of the associationsbetween the mobile terminals 110 and the base stations 115. For eachmobile unit 110, the gateway 140 can then pre-distribute packets to allthe associated base stations 115. Typically, these associations do notchange quickly; therefore, pre-distributing packets may ensure that thebase stations 115 can transmit to the mobile units 110 as soon as thescheduling and transmission formats information is made available.However, it is also possible for the control entity 135 to inform thegateway 140 of the scheduled mobile units 110 so that the gateway 140can in turn distribute packets to the respective base stations 115.

The base stations 115 may then gather or collect channel stateinformation (CSI) associated with the supported legs. In one embodiment,each base station 115 obtains per-antenna CSI parameters—such as channelgain and phase—to each mobile unit antenna with which it has a leg. TheCSI can be measured directly by the base station 115 (as in the case ofTime Division Duplex (TDD) operation) or alternatively the CSI may bereported to the base station 115 by the mobile units 110 in the case ofFrequency Division Duplex (FDD) operation. Yet another alternative isthat the CSI may be estimated by a separate element such as an UplinkIBS-MIMO Processor. The base stations 150 may also collect otherscheduling parameters including queue depth, traffic type and QoSparameters, and the like. The collected information may then betransmitted to the centralized downlink MIMO network controller 135. Inone embodiment, the quantum of information conveyed may be optimizedbased on the number of mobile units 110 deemed to benefit from IBS-MIMO.This is closely related to the process of scheduling and transmissionformat computation, described below.

Scheduling of the transmissions and/or the transmission formatcomputations may be accomplished using a variety of options. A firstoption is to transmit all of the channel state information and otherscheduling information from the base stations 115 to the centralizeddownlink network MIMO controller 135, which then schedules the mobileunits 110 and computes the corresponding transmission formats. Thetransmission formats and the scheduling information are then conveyed tothe base stations 115 for subsequent transmissions, as described herein.A second option is to distribute the computations between the basestations in the centralized downlink network MIMO controller 135. Inthis case, the scheduling parameters and channel state information for aselected subset of the mobile units 110 is transmitted to thecentralized downlink network MIMO controller 135, which then compute thetransmission formats and does the scheduling for this subset of themobile units 110. The base stations 115 then assume responsibility forscheduling other mobile units 110 and computing their respectivetransmission formats. A third option is to allow the base stations 115to perform scheduling of the mobile units 110. The base stations 115 canthen transmit the identities of the scheduled mobile units and thecorresponding channel state information to the centralized downlinknetwork MIMO controller 135, which computes the correspondingtransmission formats and conveys this information to the base stations115.

An alternative to the centralized structure is to use a decentralized,or distributed, downlink network MIMO controller 135. In the distributedarchitecture, the system 100 includes interfaces between the basestations 115 and the downlink network MIMO controller 135, the basestations 115 and the bearer plane gateway 140, and the downlink networkMIMO controller 135 and the bearer plane gateway 140. The system 100also defines additional interfaces between each of the base stations 115because the distributed downlink network MIMO controllers 135 areco-located with the base stations 115. Furthermore, protocols can beestablished for carrying different types of IBS-MIMO related messagesover the interfaces. In some cases, basic interfaces/messages aredefined in existing standards and the standards can be extended and/ormodified for IBS-MIMO purposes as discussed herein.

Examples of an additional interface between the base stations 115include the X2 in LTE/SAE and R8 in WiMAX. Since IBSMCs 135 are locatedat the base stations 115 and the distributed architecture, thisinterface can be used to convey both control and data information acrossbase stations 115 to enable IBS-MIMO. In some embodiments, the scope ofthis interface may be extended to include IBS-MIMO and new messages maybe defined as well. For example, for each mobile unit 110, the basestation 115 may use this interface to convey IBS-MIMO controlinformation to the IBSMC 135, and the IBSMC 135 may use this interfaceto convey transmission formats to all the base stations 115 that are totransmit to the mobile unit 110.

In operation, the distributed architecture may operate in a manner thatis similar to the algorithms used by the centralized architecture.However, operation of the distributed downlink network MIMO controller135 may be modified to support the distribute architecture. For example,in the distributed scenario, the mobility manager may be enhanced tomaintain a separate record for IBS-MIMO legs and inform the basestations 115 appropriately. The base station 115 with the “primary” legto the mobile unit 110, i.e. the base station 115 with the strongestleg, can be designated as the distributed downlink network MIMOcontroller 135 for that mobile unit 110. In an alternate technique thatmay be less efficient, base stations 115 may inform immediate neighborsof the mobile units 110 that they have legs to, as well as theappropriate leg strengths. Subsequently, the base station 115 with thestrongest leg can be designated as the distributed downlink network MIMOcontroller 135. Once the base stations 115 that support the distributeddownlink network MIMO controller 135 for each of the mobile units 110has been specified, operation of the distributed downlink network MIMOcontroller 135 may proceed as described herein.

Embodiments of the network architecture described herein adhere to thearchitectural principles of the major next generation standards beingdefined (e.g., LTE-SAE in 3GPP, UMB in 3GPP2, and WiMAX in the WiMAXForum). Embodiments of the network architecture described herein maytherefore enable network operators to harness the power of downlinkNetwork MIMO without disruption to existing network architectures, eventhough Network MIMO can be a disruptive physical layer technology.Further, the network architecture described herein achieves this whilecontrolling the additional backhaul bandwidth consumption due to networkMIMO-related control information. In fact, this solution allows forselective application of Network MIMO technologies to only those userswho are most likely to benefit from it, thus reducing the costs evenfurther.

Portions of the disclosed subject matter and corresponding detaileddescription are presented in terms of software, or algorithms andsymbolic representations of operations on data bits within a computermemory. These descriptions and representations are the ones by whichthose of ordinary skill in the art effectively convey the substance oftheir work to others of ordinary skill in the art. An algorithm, as theterm is used here, and as it is used generally, is conceived to be aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofoptical, electrical, or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, or as is apparent from the discussion,terms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical, electronicquantities within the computer system's registers and memories intoother data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission or display devices.

Note also that the software implemented aspects of the disclosed subjectmatter are typically encoded on some form of program storage medium orimplemented over some type of transmission medium. The program storagemedium may be magnetic (e.g., a floppy disk or a hard drive) or optical(e.g., a compact disk read only memory, or “CD ROM”), and may be readonly or random access. Similarly, the transmission medium may be twistedwire pairs, coaxial cable, optical fiber, or some other suitabletransmission medium known to the art. The disclosed subject matter isnot limited by these aspects of any given implementation.

The particular embodiments disclosed above are illustrative only, as thedisclosed subject matter may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope of the disclosedsubject matter. Accordingly, the protection sought herein is as setforth in the claims below.

What is claimed:
 1. A physical plane entity to: receive channel stateinformation for a plurality of wireless communication channels between aplurality of base stations and at least one mobile unit and queue stateinformation indicative of a status of queues for data to be transmittedover the downlink to said at least one mobile unit by each of theplurality of base stations; determine, based on the channel stateinformation and the queue state information, transmission formats forsynchronized downlink transmissions from the plurality of base stationsto said at least one mobile unit so that said synchronized downlinktransmissions combine coherently and constructively at said at least onemobile unit; and provide the transmission formats to the plurality ofbase stations.
 2. The physical control plane entity of claim 1, whereinthe physical control plane entity is to determine at least one of ablock size, an error control code, a code rate, a modulation order, anantenna beamforming weight, a transmit power, an orthogonal frequencydivision multiplexing tone, and an orthogonal frequency divisionmultiplexing tile.
 3. The physical control plane entity of claim 1,wherein the physical control plane entity is to determine timinginformation for each of the plurality of base stations based upon thechannel state information.
 4. The physical control plane entity of claim3 wherein the physical control plane entity is to provide the timinginformation to the plurality of base stations, and wherein the pluralityof base stations can transmit information over the downlink at timesindicated by the provided timing information so that the transmittedinformation from the plurality of base stations combine coherently andconstructively to amplify, at said at least one mobile unit, informationtransmitted over the downlink.
 5. The physical control plane entity ofclaim 1, wherein the physical control plane entity is to schedulesynchronized downlink transmissions from the plurality of base stationsto said at least one mobile unit.
 6. The physical control plane entityof claim 5, wherein the physical control plane entity is to jointlyschedule the synchronized downlink transmissions and determinetransmission formats for the synchronized downlink transmissions.
 7. Thephysical control plane entity of claim 1, wherein the synchronizeddownlink transmissions from the plurality of base stations to said atleast one mobile unit are scheduled by the corresponding base stationsand the physical control plane entity is to determine transmissionformats for the scheduled synchronized downlink transmissions.
 8. Thephysical control plane entity of claim 1, wherein the physical controlplane entity is to select the plurality of base stations that providecoordinated synchronized downlink transmission to said at least onemobile unit.
 9. The physical control plane entity of claim 8, whereinthe physical control plane entity is to provide, to an Internet Protocol(IP) gateway, information indicating the selected plurality of basestations so that the IP gateway can provide parallel downlink datastreams to each of the selected plurality of base stations.
 10. Thephysical control plane entity of claim 1, wherein the physical controlplane entity is to dynamically determine relative time delays betweenlegs of backhaul links between the physical control plane entity andantennas associated with the plurality of base stations, and wherein thephysical control plane entity is to determine the transmission formatsbased on the relative time delays.
 11. A base station for use as one ofa plurality of base stations, wherein the base station is to: provide,to a control plane entity, channel state information for at least onewireless communication channel between at least one antenna associatedwith the base station and at least one antenna associated with said atleast one mobile unit and queue state information indicative of a statusof queues for data to be transmitted over the downlink to said at leastone mobile unit; receive, from the control plane entity, transmissionformats for synchronized downlink transmissions from the base station tosaid at least one mobile unit, the transmission formats being determinedby the control plane entity for the plurality of base stations based onthe channel state information and the queue state informationtransmitted to the control plane entity and additional channel stateinformation and queue state information provided to the control planeentity by at least one other base station from the plurality of basestations; and transmit data over the downlink in coordination with theplurality of base stations using the received transmission formats sothat synchronized downlink transmissions from the plurality of basestations combine coherently and constructively at said at least onemobile unit.
 12. The base station of claim 11, wherein the base stationis to receive at least one of a block size, an error control code, acode rate, a modulation order, an antenna beamforming weight, a transmitpower, an orthogonal frequency division multiplexing tone, and anorthogonal frequency division multiplexing tile.
 13. The base station ofclaim 11, wherein the base station is to receive timing informationdetermined by the control plane entity based upon the channel stateinformation.
 14. The base station of claim 13, wherein the base stationis to transmit information over the downlink at times indicated by theprovided timing information so that the transmitted information combinescoherently and constructively at said at least one mobile unit withinformation transmitted over the downlink by the plurality of basestations to amplify the information transmitted over the downlink by thefirst base station.
 15. The base station of claim 11, whereinsynchronized downlink transmissions from the base station to said atleast one mobile unit are scheduled at the control plane entity, andwherein the base station is to receive, from the control plane entity,scheduling information for said synchronized downlink transmissions fromthe base station to said at least one mobile unit.
 16. The base stationof claim 11, wherein the base station is to schedule said at least onemobile unit for synchronized downlink transmissions and providescheduling information to the control plane entity.
 17. The base stationof claim 16, wherein the base station is to receive transmission formatsdetermined by the control plane entity for the scheduled synchronizeddownlink transmissions in response to providing the schedulinginformation to the control plane entity.
 18. The base station of claim11, wherein the base station is to receive information indicating thatthe control plane entity has selected the base station to providecoordinated synchronized downlink transmission to said at least onemobile unit.
 19. The base station of claim 11, wherein the base stationis to receive, from an Internet Protocol (IP) gateway and in response tobeing selected to provide coordinated synchronized downlinktransmission, at least one downlink data stream concurrently with otherdownlink data streams provided to the plurality of base stations by theIP gateway.
 20. A physical control pane entity to: receive channel stateinformation for a plurality of wireless communication channels between aplurality of base stations and at least one mobile unit; dynamicallydetermine relative time delays between legs of backhaul links betweenthe physical control plane entity and antennas associated with theplurality of base stations by transmitting a timing signal from thephysical control plane entity to the plurality of antennas and receivingechoes of the timing signal at the physical control plane entity fromthe plurality of antennas; determine, based on the channel stateinformation and the relative time delays, transmission formats fordownlink transmissions from the plurality of base stations to said atleast one mobile unit so that said downlink transmissions combinecoherently and constructively at said at least one mobile unit; andprovide the transmission formats to the plurality of base stations.